The present disclosure relates to a display apparatus and, more specifically, to a display apparatus for use as a head mounted display (HMD), for example, and also to an image display device suitable for use in the display apparatus, and a light guide unit suitable for use in the image display device.
Japanese Patent Application Laid-Open No. 2006-162767 describes a virtual image display device (image display device), for example. This virtual image display device is well known to provide two-dimensional (2D) images as enlarged virtual images by a virtual-image optical system. Herein, the 2D images are those formed by an image forming unit and provided to be viewed by viewers.
This image display device 1100 includes, as shown in the conceptual view of FIG. 38, an image forming unit 111, a collimator optical system 112, and a light guide section 120. The image forming unit 111 includes a plurality of pixels that are arranged in a 2D matrix. The collimator optical system 112 collimates light coming from each of the pixels in the image forming unit 111. The light guide section 120 guides and emits the resulting collimated light coming from the collimator optical system 112. The light emitted from the light guide section 120 is then guided to eyes 21 of a viewer 20. The light guide section 120 is configured by a light guide plate 121, and first and second deflection sections 130 and 140. The light guide plate 121 propagates therein the incoming light by total reflection, and then emits the light. The first deflection section 130 is a single-layer light reflection film, for example, and reflects the light entered the light guide plate 121 so as to achieve total reflection therein. The second deflection section 140 is a multi-layer light reflection film in the multi-layer film structure, and emits the light from the light guide plate 121 after the light is propagated therein by total reflection. If such an image display device 1100 configures an HMD, for example, the resulting display apparatus may be reduced in weight and size.
As another virtual image display device well known to provide, for viewing by a viewer, 2D images formed by an image forming unit as enlarged virtual images by an image forming unit, Japanese Patent Application Laid-Open No. 2007-094175 describes a virtual image display device (image display device) using a holographic diffraction grating, for example.
This image display device 1300 basically includes, as shown in the conceptual view of FIG. 39, the image forming unit 111 that displays images, the collimator optical system 112, and a light guide section 320. In the light guide section 320, light coming from the image forming unit 111 is guided to the eyes 21 of the viewer 20. Such a light guide section 320 includes a light guide plate 321, and first and second diffraction grating members 330 and 340. The first and second diffraction grating members 330 and 340 are each a reflective volumetric holographic diffraction grating provided to the light guide plate 321. Collimated light from the collimator optical system 112 enters a first plane 322 of the light guide plate 321, and then is emitted from the first plane 322. The light guide plate 321 has a second plane 323, which is parallel to the first plane 322 thereof. The second plane 323 is attached with the first and second diffraction grating members 330 and 340.